The present invention relates to a hydrogenation catalyst and its preparation.
The hydrogenation has been extensively applied in processes such as the hydrogenation of olefin, alkyne, aromatics, nitro compounds, carbonyl groups, nitrile groups and other unsaturated compounds, and hydrorefining of crude products such as caprolactam in chemical, especially fine chemical, engineering field. The most widely used catalyst in these processes is skeletal nickel (Raney nickel) catalyst which has been applied in the industry for many years and has become technically matured, and so long no other catalyst can substitute for it. In recent years, a widely reported amorphous alloy catalyst has shown its superiority to Raney nickel catalyst in respect of activity and selectivity with the momentum of taking the place of Raney nickel catalyst.
Amorphous alloys are a new kind of catalyst materials in which the atoms are in short-range ordered but long-range disordered arrangements, thus ensuring that the catalysts have an increased number of active sites in a uniform distribution. However, ordinary amorphous alloys have the disadvantage of low activity and small specific surface area, which cannot exceed 10 m2/g even after various chemical and physical treatments, thus its prospect of industrial application is limited. In this connection, CN1073726A discloses a process for the preparation of a large-surface-area Ni(Fe or Co)xe2x80x94Rexe2x80x94P amorphous alloy catalyst by alloying nickel or Fe or Coxe2x80x94Rexe2x80x94P and aluminum using the rapid quenching and moulding method and then leaching out the aluminum with alkali to obtain an amorphous alloy catalyst having a specific surface area of up to 50-130 m2/g which make it possible to be used in industry. In comparison with Raney nickel catalyst, the Rexe2x80x94Nixe2x80x94P catalyst has a distinctly higher activity in the saturation-hydrogenation of olefin and aromatic hydrocarbons (see CN1146443A).
CN1152475A discloses a ferric magnetic amorphous alloy catalyst consisting essentially of 45 to 91 wt % nickel, 2 to 40 wt % iron based on the weight of the catalyst and P in balance. The catalyst obtained in this manner has higher catalytic activity than the catalyst described in the CN1073726A.
U.S. Pat. No. 3,839,011 discloses a Raney nickel catalyst and its preparation. The catalyst is prepared by melting nickel and aluminum, pouring the molten alloy into a flowing water stream to be cooled. A readily crushable catalyst of low bulk density is obtained by this process. However, this process cannot provide an amorphous alloy catalyst having an amorphous structure of adequate stability.
U.S. Pat. No. 5,090,997 discloses a process for preparing a Raney nickel catalyst. The catalyst is obtained by heating the molten aluminum alloy to a temperature of 50 to 500xc2x0 C. above its melting point, atomizing the liquid melt with water or a mixture of water and gas, then cooling the atomized alloy in water or air to obtain a fine particle Raney nickel catalyst. It is difficult to obtain an amorphous catalyst having a higher degree of amorphism by this method owing to its lower cooling rate.
The caprolactam is a main material for producing nylon-6. The purification of caprolactam is a key process for producing caprolactam. The process for producing area Ni(Fe or Co)xe2x80x94Rexe2x80x94P amorphous alloy catalyst by alloying nickel or Fe or Coxe2x80x94Rexe2x80x94P and aluminum using the rapid quenching and moulding method and then leaching out the aluminum with alkali to obtain an amorphous alloy catalyst having a specific surface area of up to 50-130 m2/g which make it possible to be used in industry. In comparison with Raney nickel catalyst, the Rexe2x80x94Nixe2x80x94P catalyst has a distinctly higher activity in the saturation-hydrogenation of olefin and aromatic hydrocarbons (see CN1146443A).
CN1152475A discloses a ferric magnetic amorphous alloy catalyst consisting essentially of 45 to 91 wt % nickel, 2 to 40 wt % iron based on the weight of the catalyst and P in balance. The catalyst obtained in this manner has higher catalytic activity than the catalyst described in the CN1073726A.
U.S. Pat. No. 3,839,001 discloses a Raney nickel catalyst and its preparation. The catalyst is prepared by melting nickel and aluminum, pouring the molten alloy into a flowing water stream to be cooled. A readily crushable catalyst of low bulk density is obtained by this process. However, this process cannot provide an amorphous alloy catalyst having a amorphous structure of adequate stability.
U.S. Pat. No. 5,090,997 discloses a process for preparing a Raney nickel catalyst. The catalyst is obtained by heating the molten aluminum alloy to a temperature of 50 to 500xc2x0 C. above its melting point, atomizing the liquid melt with water or a mixture of water and gas, then cooling the atomized alloy in water or air to obtain a fine particle Raney nickel catalyst. It is difficult to obtain an amorphous catalyst having a higher degree of amorphism by this method owing to its lower cooling rate.
The caprolactam is a main material for producing nylon-6. The purification of caprolactam is a key process for producing caprolactam. The process for producing caprolactam comprises the following steps: benzene hydrogenation to cyclohexane, cyclohexane oxidization to cyclohexanone, cyclohexanone oximation to cyclohexanone oxime and Backmann rearrangement of cyclohexanoneoxime in oleum. The products obtained therefrom include caprolactam and unsaturated compounds. These by-products cannot be removed by extraction and distillation because of their analogical properties. However, the presence of these unsaturated compounds are disadvantageous because they can impair the physical-mechanical properties of the nylon-6 made by polymerizing xcex5-caprolactam, so they must be removed. During the purification of caprolactam, the unsaturated impurities are saturated by hydrogenation, while their physical-mechanical properties become distinguishable from that of caprolactam, so that these compounds are more easily removed in the subsequent extraction distillation steps. In conventional technology, Raney nickel catalyst is used, but Raney nickel catalyst, with its relatively low activity, larger amount of consumption and limited ability in removing all disturbing impurities, cannot meet the demand of the technological development.
The object of the present invention is to provide a new kind of amorphous alloy hydrogenation catalyst with high activity and high purification capability which has a higher degree of amorphism and higher stability in amorphous state and is particularly useful to hydrorefining of caprolactam, and its preparation.
The hydrogenation catalyst according to the invention comprises essentially Ni ranging between 60 and 98 wt %, Fe ranging between 0 and 20 wt %, one doping metal element selected from the group consisting of chromium, cobalt, molybdenum, manganese and tungsten ranging between 0 and 20 wt %, and aluminum ranging between 0.5 and 30 wt % based on the weight of said catalyst, wherein the weight percentages of iron and the doping element components should not be zero at the same time; and just one broad diffusion peak appears at about 2 xcex8=45xc2x11xc2x0 on the XRD patterns of the catalyst within 2 xcex8 range from 20 to 80xc2x0.
The catalyst according to the present invention comprises preferably nickel ranging from 70 to 95 wt %, iron ranging from 0.1 to 15 wt %, a metal selected from the group consisting of chromium, cobalt, molybdenum, manganese and tungsten ranging from 0 to 15 wt %, and aluminum ranging from 1 to 15 wt % based on the total weight of said catalyst.
In said catalyst according to the present invention, the nickel content of amorphous alloy is more preferably in the range from 75 to 90 wt %, iron content is more preferably in range from 0.3 to 10 wt %, a metal selected from the group consisting of chromium, cobalt, molybdenum, manganese and tungsten content is more preferably in the range from 0.5 to 8 wt %, and aluminum content is more preferably in the range from 2 to 10 wt % based on the total weight of said catalyst.
The catalyst of the present invention is obtained by allowing the liquid melt of an alloy consisting of 40 to 70 wt % nickel, 30 to  less than 50 wt % aluminum, 0 to 15 wt % iron and 0 to 15 wt % chromium, cobalt, molybdenum, manganese or tungsten to harden rapidly at a cooling rate of  greater than 1000xc2x0 C./sec, preferably  greater than 10000xc2x0 C./sec; heat-treating the rapidly hardened alloy in an atmosphere of an inert gas such as hydrogen, nitrogen and/or argon at a temperature of from about 300 to 900xc2x0 C., preferably 450 to 750xc2x0 C., for 0.5 to 5 hours; and then leaching out an adequate portion of aluminum from the heat-treated alloy with an alkaline solution.
In the catalyst of the present invention, nickel as an active constituent exists essentially in the form of amorphous state.
According to the invention, the method for preparing said catalyst comprises substantially the following steps:
(1) Preparation of a parent alloy
The parent alloy is prepared by allowing the liquid melt of an alloy consisting of 40 to 70 wt % nickel, 30 to  less than 50 wt % aluminum, 0 to 15 wt % iron and 0 to 15 wt % chromium, cobalt, molybdenum, manganese or tungsten to harden rapidly at a cooling rate of  greater than 1000xc2x0 C./s, preferably  greater than 10000xc2x0 C./s;
(2) Heat-treatment of the parent alloy
The parent alloy obtained form step (1) is treated in an inert atmosphere selected from argon, hydrogen or nitrogen at 300-900xc2x0 C. for 0.5-5.0 hours, preferably at 450-750xc2x0 C. for 1-3 hours;
(3) Activation (treatment with base)
The heat-treated alloy obtained from step (2) undergoes an aluminum leaching-out treatment with an alkaline solution, thereby an adequate portion of aluminum is removed from the alloy by the reaction of the heat-treated alloy with the alkaline solution so that the desired composition of said catalyst according to the invention is obtained; the said alkaline solution can be inorganic or organic base solution, preferably an alkali metal hydroxide aqueous solution, and more preferably sodium hydroxide aqueous solution; the treatment temperature is from ambient temperature to 120xc2x0 C., a more preferably temperature is 50-100xc2x0 C.; the treatment time is between 0.5 and 5 hours, more preferably 1-3 hours; the concentration and amount of alkaline solution is not limited, and can be determined based on the desired composition of the catalyst and the existing conditions for preparing Raney nickel catalyst of the prior art; when using aqueous sodium hydroxide, for example, the concentration of aqueous sodium hydroxide can be from 10 to 40 wt %, and then weight ratio of parent alloy/NaOH can be from 1:0.5 to 1:4;
(4) Washing of the catalyst
The sample obtained from step (3) is washed free from alkali and aluminate with water having a temperature of from ambient temperature to 100xc2x0 C., preferably 60 to 100xc2x0 C., with the resultant solution having a preferred pH between 7 and 13; the sample washed can be stored in water on ethanol, most preferably under an inert atmosphere.
The catalyst according to the present invention is designed for use in hydrogenation of olefin, alkyne, aromatics, nitro, carbonyl groups, nitrile group and other unsaturated compounds, and especially suitable for hydrorefining of caprolactam.